In fact there are a number of connections between Casals and Wagner. As early as 1889, only nine years after his revelatory discovery of Bach's Cello Suites in a Barcelona music shop, the young Casals had studied scores of Parsifal, Tristan and the Ring. These were borrowed from a musician colleague at the café where the young cellist was playing in a trio to subsidise his more serious music making. With his career in the ascendant Casals joined the cello section of the Lamoureux Orchestra in 1900 for the first Paris concert performance of Tristan, and in 1926 he recorded transcriptions for cello and piano from Die Meistersinger and Tannhäuser in America; these were reissued on CD in Music Memoria's Casals, the Victor Recordings in the 1990s.

Because of his advocacy of the stylistically conservativeEl Pessebre in his later years, Casals is often portrayed as a musical reactionary. But this view is contradicted by the repertoire he programmed with his own Orquestra Pau Casals in Barcelona in the 1920s. In addition to now largely forgotten Catalan composers such as Garreta, Granados, Albéniz, Millet, Cassadó, Enric Morera and Roberto Gerhard the concerts included works by Bartók, Richard Strauss, Mahler, Milhaud, Kodály, Prokofiev, Webern, Honegger, Schoenberg and Stravinsky. Although Casals was not a fan of twelve-tone music, Schoenberg was invited to conduct a programme of his own compositions with the Orquestra Pau Casals. Schoenberg also adapted a Cello Concerto from a music by the eighteenth-century composer G.M. Monn for Casals, although the cellist did not perform it due to a copyright dispute.